The present invention relates to contamination control devices and more particularly to an exhalation evacuation system for removing exhaled gases of a patient at medical institutions and the like.
The unrestricted exhalation into the environment from persons suffering from infectious diseases is a substantial source of contamination of persons or objects in the surrounding area. Although such problems are inherent in any social situation, the possibility of contamination or infection from a person undergoing critical care in a medical facility is particularly acute. Studies have determined that a not insubstantial number of nosocomial infections occur in persons receiving treatment at such facilities. Medical facilities generally practice relatively stringent infection control procedures. However, when critical care patients are placed on respiratory ventilator units bacteria and other infectious agents present in the patient's exhalation travel a substantial distance from the exhalation outlets of the unit. Such infectious contaminates pose a substantial health risk for other patients, medical personnel, and visitors.
Exemplary of the medical profession's recognition of such contamination problems are: Dyer & Peterson, How Far do Bacteria Travel from the Exhalation Valve of IPPB Equipment?, 51 Anesthesia and Analgesia, July-Aug. p. 516 (1972); Flournoy, Plumlee & Steffee, Volume Ventilator as a Vehicle of Airborne Bacterial Contamination from Patients, 25 Respiratory Care July, p. 742 (1980); Duberstein & Howard, Sterile Filtration of Gases: A Bacterial Aerosol Challenge Test, 32 Journal of the Parenteral Drug Ass. July-Aug., p. 192 (1978); and Irwin et al., An Outbreak of Acinetobacter Infection Associated with the User of a Ventilator Spirometer, 25 Respiratory Care Feb., p. 232 (1980).
Most ventilator units include an expiratory system or line consisting of a flexible tube that extends away from the patient for dispersion of the exhaled gases. Heretofore, the dispersion of contaminates in gases from the expiratory system has been reduced by the use of bacterial filters. Such filters are placed directly in the path of air flow in order to remove the majority of bacterial infectious agents that would otherwise be exhaled directly into the surrounding room. The unit may include other components in the expiratory line downstream of the filter, such as a conventional spirometer, or a conventional check valve that permits gas flow out of the line but which prevents atmospheric return back through the line while the patient is inhaling.
Problems associated with systems having a bacterial filter placed directly in the expiratory system air flow include their cost and service life. The expected service life of a filter in continuous use is approximately two days before replacement and disposal. Although a single filter is relatively inexpensive as a single component, over the period of time that a ventilation unit may be used the cost of constantly replacing the filters may be substantial.
Another problem associated with such systems is the accumulation of moisture within the filter media. Water accumulation increases the resistance of the filter to gas flow with a resulting increase in undesirable back pressure against the patient. This accumulation also reduces the effectiveness of the filter. In an attempt to reduce this moisture problem, such systems often provide a water trap in the expiratory line upstream of the bacterial filter.
Another approach previously used to reduce ventilator unit contamination is the use of a suction or vacuum for the partial recovery of exhaled gases. Most hospitals have a contained vacuum system that extends through the walls or floor of the building. The system provides a ready vacuum source necessary for various medical activities. This wall vacuum system has been used for the partial recovery of exhaled gases. In such systems it is mandatory to keep the system open, both to prevent the wall suction from evacuating the patient and to prevent a back pressure from occurring in the expiratory line against which the patient must exhale. Such an evacuation would be counter-productive to ventilation and might pose a substantial hazard for the patient. Since the system must remain open, infectious contaminates may escape from the system and pass unrestrained into the surrounding room. This condition may occur quite frequently in such a system since the force of exhalation varies during the cycle of a single breath.
There is a substantial need, therefore, for a contained system for treating exhaled gases emitted from respiratory ventilator units or the like. Due to the length of time that use of such a unit may be necessary, it would be highly desirable to provide such a unit with components that do not require frequent replacement in order to reduce re-occurring costs.